Method and apparatus for making lined tubing



March 24,-.1953 J. FITZ HARRIS 2,532,205

METHOD AND APPARATUS FOR MAKING LINED TUBING Filed Feb. 10, 1949 40 v a 8 \30 I5 '55 46 v 48 I57 v v 7 I63 v 44 v so I39 FlG.2 8 M Z Q Patented Mar. 24, 1953 UNITED STATES METHOD AND APPARATUS FOR MAKING LINED TUBING poration of Delaware Application February 10, 19.49, Serial No. 75,626,

Claims. I

invention. relates to methods. ofand apparatus for making multi-layer tubing.

Itis ananother object of my invention to provide a simple, inexpensive method of making electrically conductive tubing which can be readily carried out by simple inexpensive changes in existing machines.

It is another object of my invention to provide a simple machine for continuously making multilayer tubing employing for the principal layer a flexible plastic material.

It is another object of my invention to provide a simple inexpensive method of making flexible lined tubing in a single operation.

There is disclosed in this application tubing having an outer wallof a flexible plastic such as polyamides (nylon) and having a metallic inner lining which may serve as an electrical conductor. The tubing is formed by forcing heated plastic through a forming die. The forming pin located centrally within the forming die has passages therein for maintaining air pressure upon the inside wall. Powdered metal or other electrically conducted. coating is carried by the air through these same air passages to distribute the powdered metal on the inner surface of the tubing as'it is formed upon the forming pin and while. it is adherent, so that the metal powder adheres to the inner surface. of the tubing. In a modified form the forming pin is provided with a second set. of passages for. applying material uponand-covering thepowdered metal surfaceof theinnerwall of the tubing.

Further objects and advantages of. the present invention will be apparent from the following description, reference being had to the accompanying drawing, whereina preferredLform of the present invention is. clearly shown.

In the drawing:

Fig. 1 is a vertical sectional view, partly diagrammatic, illustrating my metal lined tubing together with. a method of and apparatus for making the tubing; and

Fig. 2 is a vertical sectional view, partly diagrammatic, illustrating a modified form of the invention in which the metal lined tubing has an additional inner. layer which is formed as the tubing is formed.

Referring to the drawing and more particularly to Fig. 1, there is shown a seamless plastic tube 20' having its inner wall lined with a seamless metallic electrical conducting material 22, such as iron or copper powder imbedded in the inner surface of the wall of'the plastic tubing 20. The

seamless plastic-tubing 20'may be formed of thermoplasticmaterial such as one of the following materials: polyamides (nylon) compounded'natural rubber; compounded synthetic rubber; polyethylene; vinylidene chloride and its co-polymers; vinylchloride and its" polymers; cellulosic esters, and ethyl cellulose; This form of metallic lined tubing provides a large metal surface for conducting electrical energy particularly at high frequencies. It may also'be used for conducting fluids;

My improved seamless tubingmay be readily made by a slight modification of a screw extrusion machine. As shown in Fig. 1 the cylinder contains heated plastic 26 which is forced by the screw, not shown, to'the die 28. Centrally located relative to the die 28 is a forming pin 30 which pierces the hot plastic 25 as it flows toward the die 28. The forming pin 30 is connected to an air or nitrogen supply duct 32 connecting with an air or nitrogen passage 34 extending axially within the forming pin 30. Radial passages 36 extend from the passage 34 to an annular groove 38 at the exit end of the forming pin 30. Air or nitrogen under pressure is supplied through the duct 32 and the air passages 34 and 36 to the groove 38 in order to support the interior of the tubing 26 as it is being formed. The free end of the tubing 20 may be capped or pinched shut or connected to a valve or a vacuum machine. Also upon the outside of the tubing 20, as it leaves the forming die 28, there is a section 40 which is supplied with air or nitrogen under pressure through the entering duct 42 under the control of its valve 44 and the valve 36 in the exit duct 48. This supply of air or nitrogen prevents the tubing, from adhering tothe cylinder. section ll) as the heatedplastic isextrudedfrom the forming die 28.

Adjoining section his a coolingvsectionfill pro.- vided with .cooling passages throughwhich water or other. cooling fluid is circulated. The forming die 28 is also provided with passages through which oil or steammay be circulated to ,controlthe temperature of the Wall surfaces in contact with the heated plastic 25.

According to my invention instead of supplying only air or nitrogen to the interior of the tubing I supply along with the air or nitrogen an electrical conducting material such as iron or copper powder or aconductive coating liquid. The air or nitrogen is supplied through a duct 52 having a branch duct 54 connecting with the'valve all and a branch duct 56' provided with a valve 58 connecting with a supply chamber 69. This supply chamber 60 contains the powderedmetal 62, such as iron or copper powder or other electrical conducting material in an amount Sufiicient' for a roll of tubing or more. The chamber Bil-is provided with a hollow valve member 64 at its lower outlet. The hollow stem 66 of the valve member 64 is threaded and provided with a handle 68 so that it may be raised or lowered to adjust the amount of powdered metal which passes through the outlet. The valve 58 connects with the interior of the hollow stem 50 of the valve 64. When the apparatus is in operation the air or nitrogen passes through the valve 58 and through the hollow stem 66 of the valve 04 and mixes with the powder flowing out of the bottom of the chamber 60. The air or nitrogen and the powder are mixed in a Venturi mixing chamber I beneath the chamber 60 and an additional air or nitrogen supply is provided at the outlet of the Venturi mixing section by a branch air or nitrogen line 12 under the control of the valve 14.

As the heated plastic 25 flows around the forming pin 30 within the forming die 28, it is brought to the proper temperature so that the tubing is properly formed as it leaves the die 28. However, as it leaves the die 28 the plastic is still in an adherent condition and must be prevented from sticking to the walls of the section 40 by the proper supply of air or nitrogen through the duct 42. The interior of the tubing must also be supported by a continuous supply of air or nitrogen. According to the invention, however this cont'nuous supply of air or nitrogen carries with it the metal powder which is discharged against the interior wall of the tubing as it forms so that the metallic coating thus provided adheres to the ining surface of the tubing as it is formed and forms seamless electrically conductive surface of large area. Since the surface of electrical conductors are the most eificient portion of the conductor, this form of tubing provides a very efficient inexpensive form of electrical transmission. Instead of employing a dry metal powder, any continuous film-forming liquid heavily pigmented with metallic particles may be employed. For example, there may be used a high boiling point plasticizer heavily pigmented with iron, copper .and/ or aluminum powder.

In Fig. 2 the seamless tubing I20 is made of similar plastic material and contains an inner seamless metal lining I22 similar to that disclosed in Fig. 1. However, in addition the tubing is provided with an additional seamless inner sleeve I23 preferably of a very soft flexible adherent plastic. This layer I23 may be formed of one of the plastics mentioned above for the tubing 20. However, it is preferred that the plastic flow more readily than the plastic used in the tubing 20 and I 20. If the same plastic is used for both the tubing I20 and the layer I23 it is preferred that the material for the layer I23 be more highly plasticized. In this form the cylinder 24, the forming die 28 and the cylinder section 50 are the same as shown in Fig. 1 and perform the same function. The section I40 is, however, longer than the section 40 and the forming pin I30 is provided with coaxial passages I33 and I34. The passage I34 is fed from a metal powder m xing system including the Venturi member I0 through the supply conductor 32 with metal powder and air or nitrogen in a manner similar to that illustrated in Fig. l for the air and metal powder supply. However, in Fig. 2, in addition to the air or nitrogen and metal powder supply, the second passage I33 is supplied with plastic material through the supply duct I35. Two alternately operative chambers I59 and I6I are each provided with an air or nitrogen supply from the air or nitrogen supply line I under the control of the valves I53 and I55. The material for the chamhere I 59 and I3I is supplied through the entrance members I57 and I58 which are also provided with valves for sealing the chambers I59 and it I. The outlets of the chambers I59 and IOI are connected to the supply duct I35 under the control of the valves I53 and I65. The chambers I59 and IGI are used alternately, first one is filled and used and while it is being used the second is filled ready to be cut in when the first is exhausted.

The air supply duct I34 discharges thrOugh ra1 dial passages into an annular groove I38 while the passage I33 discharges through radial passages into annular groove I33. The groove I38 applies the metal powder carried by the air or nitrogen to the inner wall of the molten plastic I26 as it emerges from the die 28, while it is yet adherent. The plastic material forced into the groove I39 coats the interior of the tubing and thereby covers the metal powder I22 with a layer I23. This layer I23 protects the meal powder I22 and insulates it from any fluid in the tubing. The air or nitrogen within the tubing supports it while the air or nitrogen within the section I40 surrounding the tubing prevents the tubing from adhering to the wall of the section I40. By the time the tubing reaches the cooling portion 50 it is cooled sufficiently to prevent it from adhering to its walls.

While the form of embodiment of the invention as herein described, constitutes a preferred form, it is to be understood that other forms might be adopted, as may come within the scope of the claims.

What is claimed is as follows:

1. The method of making lined tubing which includes extruding heated plastic in the form of tubing and cooling the extruded tubing until it is capable of holding its shape, applying an inner lining of a different material as the heated plastic is formed into tubing and .before it is cooled materially while the plastic is still adherent so that the lining is bonded to the interior of the plastic tubing and applying a second inner lining of a heated plastic material over the first lining to protect the first lining.

2. The method of making lined tubing which includes continuously extruding heated plastic in the form of tubing. continuously progressively cooling the tubing after it has been formed, continuously applying thin metallic wall to the interior of the tubing before the tubing is cooled while it is yet adherent to provide plastic tubing having an adherent inner metallic wall in the form of a hollow inner sleeve, and continuously applying a heated adherent plastic coating to the inner surface of said metallic wall as said metallic wall is formed.

3. A means for making lined tubing including an extruding means provided with a forming die, a forming pin centrally located within the forming die to form the extruded material into tubing, said forming pin being provided with an annular groove and supply passages extending to said groove for applying a second material to the inner surface of the tubing as it is formed.

4. A means for making lined tubing including an extruding means provided with a forming die, a forming pin centrally located within the forming die to formthe extruded material into tubing, said forming pin being provided with spaced annular grooves and separate supply passage extending to each of said grooves for successively applying layers of material to the inner surface of the tubing as it is being formed.

5. The method of making lined tubing which 5 includes extruding in a fiowable fused state of high plasticity heated plastic in the form of tubing and cooling the extruded tubing until it is capable of holding its shape, forcing an electrical conducting material directly radially relative to the axis of the tubing into direct adherence with the inner surface as the heated fiowable fused plastic is formed. into tubing and before it is cooled materially while the plastic is still adherent so that the electrical conducting material is bonded to and forms a lining upon the interior of the plastic tubing.

LEO J. FITZ HARRIS.

REFERENCES CITED The following references are of record in the file of this patent:

6 UNITED STATES PATENTS Number Number 15 244,280 

